WoW Classic and Cataclysm Classic
Unlooted items in WoW Classic and Cataclysm Classic are not sent to your mailbox. Items that aren’t looted will remain on the corpse until it despawns. Customer Support does not recover unlooted items.
You left the dungeon, therefore, forfeit the loot. Sorry, but there’s nothing anyone can do to help you.
I don’t recall the “looking for group” menu in this game 20 years ago.
Then this needs to change. There is no excuse this should still be a thing in a 20 year old game. This does nothing good for the game. This is not good for the players. This should not exist.
Unless you’re talking about retail, then there’s nothing to change - folks wanted the classic feel; flaws and issues. And Blizzard made it clear that the loot and mail system that you want is a retail feature, not classic.
If you want to give your feedback, you can hit up the classic general forum for that. CS has nothing to do with game improvements and the folks who take feedback don’t come here.
Was the LFG menu in classic WoW?
It exists because fixing it, or changing it, both breaks the “no changes” philosophy Classic started with (“bug-for-bug compatibility” is a thing), and requires the resources of developers who are busy doing other things that their managers have decided have more marketable and shareholder value.
Lately I’m just finding more reasons not to play WoW than to keep playing it. This certainly doesn’t make me happy to continue playing it knowing I can waste time and lose loot because another player decides to go afk inside a dungeon. I shouldn’t be expected to remember this every time I do a dungeon.
After today’s tantrum, you’ll probably remember.
Certainly, that’s a reasonable perspective. If the game fails to satisfy you that much, you should definitely stop paying for an unsatisfactory product.
But that’s not any kind of leverage, you understand. Blizzard isn’t going to chase after you begging you not to leave. If you leave, it needs to be because you’re sincerely done with it, not because you want to make a soulless corporation jealous.
Nah. I won’t, because I shouldn’t have to. This is a problem and it needs to change. I don’t care if you see it as a tantrum. It needs to be said so these things don’t remain a problem in a 20 year old game.
This is not the forum for such feedback.
It is not a problem in Retail at all. As others have said, you chose to play Classic #NoChanges.
This is not a discussion about retail. I don’t care about retail. And please don’t be snarky with your little “you chose to play classic” rant. I don’t care to hear it, because as you said, this is not the forum for such feedback. 
As you’ve noticed this is not the forum for such feedback. I recommend the Classic forums if you want to suggest changes to the automated item return system that was implemented in later Retail to be added to Classic.
It DID change. As others said though, you decided to play the version of the game that has some serious limitations. Those have been the limitations for 20 years, and still are. They have support articles just to ensure you still remember that.
It sucks to not get loot. It sucks that it was not your fault. Nobody said otherwise. It is/was worth putting in a ticket just in case they MIGHT be able to help.
I would not expect it though given the limitations on Classic.
You want a change post in classic general
I think me having to even do that in a 20 year old game is pretty lame. If the difference in this problem being fixed, in a 20 year old game, is me going on the classic forums making a suggestion to have this problem fixed, then I think they really need to change how they do things.
They did fix the problem, it is called retail now. But your playing classic before it was fixed
I don’t think Blizzards needs to, after extensive feedback from players they added LFD for example. This is important to voice your opinion on matters, respectfully.
You are however, not the only person who wants or doesn’t want this change.
But that’s the thing. Players wanted the original classic experience. That’s the whole POINT of their comment to you.
Just because you don’t want to hear it doesn’t make it snarky or untrue.
If you want to see a change, since you keep saying “This has to change” - make the suggestion via the appropriate avenues for devs to consider.
Stop trying to use the 20 year old game as an excuse though. Classic is classic. The retail game is the current version with ALL the changes since it came out.
There are NO devs here.
There are NO community managers here.
So you want change but don’t want change then?
If your posts are too long and didn’t get read, I suggest you to shorten it so it’s more readable for feedback 
While you are always welcome to ask, sometimes the answer is going to be we cannot do that.
If you’d like to see changes, this is just not the forum. Given all the excellent information you’ve already been given I think it’s time to wrap this one up.